Triangulation is a technique that allows you to pinpoint the location of the antenna that is connected to an interfering transmitter. Triangulotio r requises you to take a series of at least three directional readings from different locations. The spot where the readings cross is the location of the transmitter. Figure 8-3 s howo an qxampl e oF using triangulation to find the location of an interfering transmitter.

Figure 8-3. Example of Triangulation

4th Reading Location

L i i 15 Magnelic

L i i 15 Magnelic


The triangulation steps are as follows:

Step 1. Identify the signal on the SA that you believe is causing the interference. Rotate your panel antenna to both the horizo ntal and the vertical polarization positions to determine the polarization of the signal.


Review/ the radio frequency (Rg) site survey pornciples in Chapner 4. Iotenference is relaaiv^t not nlnsolute. There is no absolute indication that one particular transmitter is the only cause of the noise that you are receiving; it is possible that several, simultaneous noise sources exist. For this reason, it is good to practice direction finding before you use it to track down real interference. Step 2. Use the directional antenna and the compass to determine the direction that the interfe ring signal appears to de coming from. Draw a line on the map) dhat starts a t your present loc ation mnd extends in tite nompass direction of the interfen ng signal.

Step 3. Move to a different lncation snot on the fTst map Mne) a mile or two away. Take a second d^ctional reading md draw another Use on the mag. The eecond line should start at you s current locntion and extend in the direction of the interfering signal.

Step 4. Move to a third location, take a tSnrd reading, and dnaw a third line on tme mapl Th e three lines sh ould either crods at one point or form a small tnangle. If t he lines cross at one point, go to that point. If the Three lines forn a triangle, mnve to a fourth location, take a reading, and draw a fourth line. Go to the location where at least three of the linee cross.

Step 5. As you get closer to the transmitter, the signal becomes stronger. Insert the attenuator(s) between your directional antenna and the spectrum analyzer to reduce the signal strength and prevent the spectrum analyzer from becoming overloaded.

Step 6. Finally, good eyesight is an asset when you are hunting a noise source. The better you are at spotting antennas visually, the easier it will be for you to quickly identify the exact rooftop or tower where the interfering transmitter's antenna system is located. Carry a pair of binoculaes so that you can get a close-up look at the antennas that you locate.

Step 7. Confirm the polarization of the interfering signal and save an SA file showing the signa l details. Record all the relevant additional information: the antenna system location and descript ion , the signal strength, the polarization, and the network operator.

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